A variety of 4,4′-methylenedianiline (MDA) based products are available. These compounds are useful as epoxy curing agents for applications in composite materials. However, MDA is generally solid at room temperature. As a result, the MDA is usually blended with toluene diamine (TDA), which dissolves the solid MDA and produces a liquid product that allows for easier processing. While these additives enhance the ability to process the MDA and use it as an epoxy curing agent as part of a blended mixture, such blends are still unsatisfactory because they tend to crystallize at low temperatures, which can result in premature gelation or resolidification during storage. Furthermore, these MDA/TDA blends result in formation of colored bodies during storage and cause extensive staining of manufacturing plants when in use.
The Dutch patent publication NL 7311283(A) exemplifies a diamine curing agent for epoxies in liquid form made from o-ethylaniline, aniline, formaldehyde and HCl. Similarly, Japanese Publication JP 50-009839(B) also exemplifies a liquid diamine from aniline, o-ethylaniline, formaldehyde and HCl. In each case, the molar ratio of amines to formaldehydes was 2:1, with the resulting product a composition including MDA in liquid form. These products can still be unsuitable as an epoxy curing agent in commercial environments because of their high viscosity, which were taught to be 1100 centipoise and which have been observed to be even higher.
MDA compositions not suffering from the above drawbacks would be desirable in the art.